Because of the anatomical fact that the arm normally has a valgus orientation and load, mild varus instabilities remain unnoticed clinically. Mild valgus instabilities are more likely to be present.
Reproducing the actual subluxation, and the clunk that occurs with reduction, usually can only be accomplished with the patient under general anesthesia or occasionally after injecting local anesthetic into the elbow.
Varus instability of the elbow is acutely due to rupture of the lateral collateral ligament from subluxation of the elbow or from instability due to a lateral collateral ligament injury that has failed to heal properly.
Rarely, one sees instability in people who are chronically dependent on walking sticks or in patients in the context of surgery for lateral epicondylitis or surgical repair of a radial head fracture.
Posterolateral instability occurs with rupture of the lateral collateral ligament. Because of the anatomical fact that the arm normally has a valgus orientation and load, mild varus instabilities remain unnoticed clinically. Mild valgus instabilities are more likely to be present.
O’Driscoll SW, Bell DF, Morrey BF: Posterolateral rotatory instability of the elbow. J Bone Joint Surg Am. 1991 Mar; 73(3):440-6. PMID: 2002081
William Regan, Peter C Lapner: Prospective evaluation of two diagnostic apprehension signs for posterolateral instability of the elbow. J Shoulder Elbow Surg . May-Jun 2006;15(3):344-6. doi: 10.1016/j.jse.2005.03.009. PMID: 16679236
Lauren E. Karbach, MD and John Elfar, MD: Elbow Instability: Anatomy, Biomechanics, Diagnostic Maneuvers, and Testing. J Hand Surg Am. 2017 Feb; 42(2): 118–126. PMID: 28160902
Clinical Tests for the Musculoskeletal System 3rd Edition.
Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.